1. Field of the Invention
This invention relates to an automatic guiding method and a device for a work piece in a sewing machine, which automatically adjusts the side edge of a work piece being sewn during the sewing operation of the machine so as to maintain the side edges in a proper position, whereby a work piece may be stitched at a given distance from the side edge of the work piece.
2. Description of the Prior Art
An attempt has been made, as disclosed in Japanese Pat. No. 430726 (Japanese Patent Publication No. 7688/64), to position a detecting means at a given transverse distance from the feeding line of a work piece, which passes through a stitching point, but upstream of the stitching point. In addition, a feeding control device for a work piece is positioned further upstream of the detecting means so as to be rotatable about an axis running substantially parallel with the aforesaid feeding line, and includes a single rotary wheel adapted to be driven by a servomotor the normal and reverse rotations of which are controlled by the aforesaid detecting means. Thus, the aforesaid detecting means detects whether or not the side edge of a work piece being fed in a given direction during the sewing operation of the machine is maintained in a proper position or biased in either direction from the feeding direction, after which the rotary wheel in the aforesaid feeding control means is rotated according to a deviation signal from the detecting means so as to bring the side edge of the work piece back to a proper position. To achieve this the rotary wheel maintains its contact with a work piece.
Another attempt has also been made, in which in place of a feeding control device for a work piece, a mechanical stop member is provided in a predetermined proper position, and through which a work piece is to pass, but upstream of the stitching point of a work piece; and a resisting means is positioned upstream of the stop member but opposite to the stop member with respect to the feeding line of the work piece, which passes through the stitching point of the work piece, so that the resisting means presses the surface of the work piece, whereby during the sewing operation of the machine, the work piece has imparted thereto a moment of rotation in the counterclockwise direction about the stitching point of the work piece at all times so that the side edge of the work piece will maintain contact with the stop member for keeping the side edge in a proper position.
However, these attempts suffer from the following shortcomings:
Firstly, in the former attempt, if the wheel is small the peripheral speed of the rotary wheel in the normal and reverse directions must be increased for controlling the side edge. In addition, an increase in the peripheral speed requires an acceleration of the response of the control system to the detecting means. This is because if the aforesaid response is not sufficiently prompt relative to the peripheral speed of the rotary wheel, then the stitching line relative to the side edge will deviate, thereby failing to provide a stitching line on a work piece at a given distance from the aforesaid said edge. For this reason, even if a non-responsive zone for maintaining the rotary wheel in an inoperable condition is provided in the detecting means, the width of the zone appears as a control error for the position of the side edge, due to the high responsiveness of the control device and the increased peripheral speed of the rotary wheel. For this reason, the width of the zone can not be enlarged sufficiently for obtaining a desired stitching line with the result that the frequency of changing the direction of rotation of the servomotor for driving the rotary wheel is greatly increased, thereby causing a large current flow, thereby shortening the service life of the servomotor, causing a problem in its durability.
Secondly, as has been described earlier, the desired control of the side edge of a work piece over a wide range dictates an increase in peripheral speed and high responsiveness. In an attempt to attain the aforesaid object by rotating the rotary wheel either in the normal direction or in the reverse direction, the following shortcomings arise. As shown in FIG. 13A, the rotary wheel should operate in response to the side edge a of a work piece W, even if the rotary wheel fails to respond to a frayed spot b produced on the side edge a, when the work piece is cut. Conversely, when the rotary wheel can not respond to the frayed spot, then the rotary wheel cannot operate so as to control in response to the portion of the side edge where no fraying is produced. In either case, the desired stitching line c can not be achieved. In case the side edge a includes a discontinuity, such as shown in FIGS. 13B and 13C, where, for example, work pieces W are stitched together on their superposed portions d, a desired stitching line c as shown and which could be obtained manually can not be achieved.
Thirdly, when the rotary wheel is used for control by rotating it in the normal direction or reverse direction, it is difficult to provide a control system which provides a desired responsiveness relative to the peripheral speed of the rotary wheel. When the feeding speed of the work piece is increased as in the case of an industrial sewing machine or the like, or when the position of the side edge of the work piece is controlled, there is a deviation of the desired stitching line, even if the width of an non-responsible zone in the detecting means is minimized. For this reason, when the shape of the stitches, such as a fancy stitch, is of importance, then the feeding speed of the machine should be reduced, even at the sacrifice of operational efficiency, and in addition the peripheral speed of the rotary wheel should be reduced.
In addition, in the attempt wherein a work piece is given a moment of rotation about the stitching point by means of the resisting means so that the side edge of the work piece is maintained in contact with the mechanical stop mechanism for positioning the same properly, the following shortcomings arise:
Firstly, even after the side edge of the work piece has contacted the stop member, there still remains a moment of rotation acting in a direction to urge the side edge of the work piece towards the stop member, so that in the case of a soft work piece, the side edge of the work piece is buckled at the point of contact with the stop member, thereby failing to provide the desired stitching line.
Secondly, in the case of a work piece having a side edge with waves having a small radius of curvature, the moment of rotation should be increased for a convex portion, and decreased for a concave portion. However, it is quite difficult in practice to adjust the moment of rotation acting on the work piece by detecting the shape of the side edge of the work piece during the sewing operation of a machine so as to change the pressing force of the resisting device. Particularly, an excessive moment of rotation results in the buckling phenomenon at the side edge of the work piece at the position of the stop member, and thus this attempt is not practical.
For these reasons, the aforesaid attempts only find application in situations where the side edge of the work piece has a large radius of curvature and the work piece is relatively stiff.
Meanwhile, there arises a need to stitch two sheets of fabric in superposed relation, with the cutting edges of the fabrics being in alignment with each other. However, in such a case, the starting and terminating points for stitching sometimes become out of alignment, as shown in FIGS. 17B and 17C. This stems from inaccurate cutting, inaccurate feeding mechanism on the sewing machine, and undesirable shifting of fabrics due to the type of materials thereof. Sometimes, one of fabrics is cut longer than the other.
In a manual sewing operation, as shown in FIGS. 18A to 18D, the stitching past such an edge discontinuity is carried out along a smooth stitching line over a distance sufficient to take into account the discontinuity. Referring to FIGS. 18A to 18D, F indicates the direction of feed of the fabric, A is the starting point, and B the end point of such a smooth stitching line. FIG. 18A and FIG. 18C show stitches sewn by a sewing machine, and FIGS. 18B and 18D show overlock machine-stitches.
According to the prior art automatic guiding method, there are obtained stitching lines or stitches as shown by broken lines in FIGS. 19A to 19C. FIG. 19A is for the case where the work piece is forced against the mechanical stop, FIG. 19B is for the case wherein deviation of the work piece in the direction toward or away from the control line is controlled according to a signal from an edge detecting means, and FIG. 19C is for the case where only deviation of the work piece in the direction away from the control line is controlled according to a signal from the edge detecting means, while deviation of the work piece in the direction towards the control line is controlled by means of a stop.
FIGS. 19A to 19C show stitches formed in the standard condition according to the prior art methods. The letter F indicates the direction of feed of the fabric, and P and Q indicate the starting point and a terminating point of the stitches around the stepped portion. The fabric on the left side of the figures has a descending step portion, while the fabric on the right side has an ascending step as viewed from the feeding direction.
In FIGS. 19A to 19C, the positional relationship between the spacing between the control starting point P and the control terminating point Q, and the stepped portion does not vary to a large extent, when changing the shapes of elements, correcting speed, responsiveness and mutual positional relationship of the device. This can be seen easily by actually inserting fabric or by watching the shifting of fabric on the table. More particularly, the prior art attempts are ineffective for stitching of fabric having such a stepped portion. The major reason for this is the short correcting space, and is due to the fact that the control starting point corresponds with the stepped portion as can be seen from FIGS. 19A to 19C. One solution to the short correcting space is to increase a radius of curvature of the cut edge of the fabric and then reduce the maximum fabric shifting speed. However, the provision of a correcting space sufficiently large for smoothing the line of stitching requires the supply of fabric having a substantially linear edge, and thus this solution is not practical. It follows from this that the supply means should be improved so as to lower the fabric shifting speed to provide a sufficient spacing only upon detecting a stepped portion. In addition, one solution to the difficulty caused by having the control starting point at the stepped portion of the fabric is to detect the discontinuity ahead of the adjusting the position of fabric, i.e., before the discontinuity in the fabric comes to the fabric guiding means, thereby controlling the fabric guiding means or the discontinuity. With the prior art automatic guiding methods and devices for use in a sewing machine, when the cut edge of a work piece includes a discontinuity, there may be obtained stitches spaced a given distance from the contour of the edge of the fabric, so that, as shown in FIGS. 19A to C, staggered stitches are produced at the discontinuity and in the worst case, the stitches run off the fabric. Accordingly, for avoiding the aforesaid shortcomings, there should be provided an electrical, optical or other detecting means which detects a discontinuity in the fabric, before adjusting the position of the fabric. As a result, there should be provided a special means for controlling the position of fabric only at the discontinuity, and such means is costly and complex.